Another issue I've not encountered before...it seems it's something to do with "Power Reporting Deviation" in HWInfo. The values showed as red which caused me to look up when that meant.
Basically the value should be 100% when the CPU is fully loaded, but in my case it goes to 115%. HWInfo help bubble says anything below 90% and above 110% is of concern. The result is the system thinks the CPU is receiving more power (when it isn't) and thus throttles back to reduce load. There's a Gamer's Nexus video on subject from June 2020 for anyone interested:
I'm not sure if the issues are related, but I'm assuming it's a possibility.
I think the issue lies with the motherboard, as it was originally running a Ryzen 4300GE (basically a Ryzen 3100X with Vega 6), and Windows are installing painfully slow. I switch out to the Ryzen 2700X to check if the CPU was at fault, which did seem to speed up install, but still seemed more sluggish than it should typically have been. Then I opened task manager and noticed the listed CPU speed. This stays fixed at 0.52Ghz across all cores even when using Prime95, and as a result is limited to 17.34W powerdraw on full load (reported by CoreTemp and HWInfo).
Fortunately it's only a basic MSI A520M-A Pro, so it's not a major loss. Curiously however it did boot with typical speeds (3.9Ghz) at one point, but then reverted back to 0.52Ghz after a windows update.
Any thoughts as to how I might try fixing it, or shall I just write the motherboard off?
The BIOS is fully updated, and I'm running AMD Balanced Mode in Windows 10 Pro, Power mode makes no difference. A520 chipset drivers are also installed, BIOS has been reset to default values.